Intro

    On 11mar22 the new sband filter was installed in the postamp chassis in the pedestal. The sband inputs to the postamp chassis were connected (with no pads at the input). The field fox spectrum analyzer (SA) was used to measure the spectra in the postamp chassis (polB mainly)n starting around 9:35 ast.. During these measurements, the xband input to the postamp chassis was terminated in 50 ohms (this only affected the total power into the FO xmiter. The spectra at the output of the FO rcvr were also measured (later in the day).

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The spectra:

Postamp chassis spectra

 
 The first plots show the sband spectra at the postamp chassis (.ps)  (.pdf)

• the telescope was pointed at : az,el: 170,30deg.
  
• The sun ranged from az,el  111,40 to 126,55 during the measurements.
  
• TopFrame:  sband spectra at input to the postamp chassis (polB)
  
• SA setup: rbw 1 MHz, span 1GHz, 1001 pnts, preamp on, 5db attn
  
• Black is a single sweep, red is a peak hold (probably a few minutes), green is the noise floor of the spectrum analyzer with this setup
• the black single sweep is sitting at the noise  floor of the SA.
• There is power from 1800 MHz to 2700 MHz.
• The largest signals  are
•  2110-2155 (Advanced Wireless Band 1 AWS1)
• 2350-2360 (Wireless Communication services WCS)
• see fcc wireless bands (pdf)
• 2ndFrame: spectra after the sband filter in postamp chassis
• SA setup: rbw 1 MHz, span 1GHz, 1001 pnts, preamp on, 0db attn
• Black: trace average 10 sweeps, red  peak hold. green is the noise floor of the SA.
  
• The slope in the band and the jump at 2600 is probably the spectrum analyzer (the jump is a band change).l
• 3rd Frame. after the sband filter, blowup in freq.
• SA setup: rbw 30 KHz, span 200MHz, 1001 pnts, preamp on, 0db attn
• Black: trace average 10 sweeps, red  peak hold. green is the noise floor of the SA.
• the noise floor  of the plot is still being determined by the SA noise  floor.l
• bottom Frame: Output of diplexor, before7db  pad and FOTx input
• SA setup: rbw 30 KHz, span 200MHz, 1001 pnts, preamp on, 0db attn
• Black: trace average 10 sweeps, red  peak hold. green is the noise floor of the SA.
• the gain from the 3 amplifiers put the spectra well above the noise floor  of the spectrum analzyer.
• the purple lines show the noise floor and median of the spectrum
• the spectra show a dynamic range of about 23 db  above the noise floor(-98dbm in 300KhzRbw).
• Integrating the spectra (by multiplying the mean value  by bw/300Khz gives
  
• -55.5 + (alog10(135/.3) = -55.5 + 26.5 = -29dbm
• Adding the 7db atten would give -36dbm at input to the FOtx from sband
  
• the power meter measured -25dbm. the difference is 11 db. could this be the noise power over the 10ghz?
• alog10(10ghz/.3MHz)*10=45 db

Equivalent noise Temperature at input to FO tx

• location Using PolB	pwr/rbw dbm	rbw	bwDbHz	dbm/hz	equivalent Temp DegK	notes
  output diplexor	-55dbm	300Khz	54.77	-109.8	758.6e6	11mar22 spectra
  input to FO tx (after 7db pad)	-62dbm	300Khz	54.77	-116.8	152e6	just add 7db pad
  output FO rcvr					1.2e6	computed from fo tx,rx gain,NF measuremetns gain -21db ,NF 28db (152e6 + 182.687e3)*10^(-2.1)
  	-82.3dbm	300Khz	54.77	-137.1	1.4e6	measured with spectrum analyzer

•  
• The measured spectral values agree with the gain,NF of the FO tx,rx pair
• To get this same value at input to FO tx, we need and input temp to lna of about 100K.
  

Fiber Optic rcvr output spectra

    The 2nd set of spectra were taken downstairs at the output of the fiber optic rcvr (.ps)  (.pdf)

• The xband signal was plugged in upstairs, but the spectra are only looking at the sband portion of the signal.
• SA setup: rbw 30 KHz, span 200MHz, 1001 pnts, preamp on, 0db attn
• These spectra only show the sband portion of the FO  output.
  
• Top 2 frames: sband spectra at  output of the FO rcvr.
• top polA
• bottom polB
• black is avg 10, red is peak hold, green is the spectrum analyzer noise floor.
• The noise floor of the spectra are being set by the SA.
• The dynamic range is about 12-14 db
• Bottom 2 frames: output of udc mixing chassis.
• 2270 has been mixed to an IF of 1500 MHz
• the average in band spectral density has increased by about 34 + (15,20) db (since the 15,20db pads were still in place.
• The noise floor of the spectra are well above the noise floor of the SA (-98db in 300KHz rbw).
• The dynamic range remains at around 13db.

Summary

• The output of the lna sees signals from 1800 MHz to 2700MHz.
• the largest signals are aws-1 2210-2260 and wcs 2340-2360.
  
• At the output of the diplexor the sband bandpass had 23db of dynamic range (xb was unplugged)
• At the output of the FO rcvr the sband portion of the spectra only had  13 db of dynamic range. (xband was  plugged in upstairs).
  

processing: x101/220311/sbpwr12m.pro